This research program is devoted to study of the visual system, largely at the level of the retinal receptors. Studies on arthropods include microphotometric measurements of visual pigment absorption and fluorescence in isolated crustacean rhabdoms, the distribution of color receptors in arthropod ommatidia, and the relationship between membrane turnover and visual pigment regeneration. Studies on the avian retina include measurements of cone oil-droplets, possible visual pigments of cones, and spectral sensitivity in the violet and near ultraviolet.